JPH0495245A - Protective layer for magneto-optical recording medium and formation thereof - Google Patents

Abstract

PURPOSE:To obtain a protective film having a low residual film stress by forming a protective layer by using a chemical vapor phase deposition (CVD) method utilizing electron cyclotron resonance (ECR) plasma. CONSTITUTION:The protective layer is produced by using the electron cyclotron resonance (ECR) plasma CVD method. The deposition rate of the protective layer is improved and the residual stress in the protective layer is decreased by controlling CVD conditions. Gases are dissociated by the plasma and thin films are formed by a vapor reaction in this case and, therefore, the film quality depends largely on the production conditions, such as reactive gas flow rate, reactive gas ratio and charging power; for example the film stress is controllable to a wide range to compressive stress stress free tensile stress. The control of the film characteristics, such as refractive index, internal stress and adhesive strength, is possible in this way and the good-quality thin film suitable to the protective film for optical disks is formed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a magneto-optical recording medium that records and erases information by irradiating a laser beam and causing a magneto-optical change in the irradiated area. It concerns the material and formation method of the layer.

(Prior Art) Recently, rewritable magneto-optical disks, which record and erase information by irradiating a thin film-like magnetic medium on a substrate with a focused laser beam to create a reversal of magnetization in the thin film, have been developed for high-density, It is attracting attention as a new technology that enables large-capacity recording.

This magneto-optical recording medium uses an external magnetic field to
A thin film recording medium is irradiated with laser light and heated above the Curie point (or Neel point) to reverse the direction of magnetization, recording and erasing information, and changing the Kerr rotation angle θ based on the magneto-optic effect. Information is reproduced by reading changes. Usually, the material of the recording layer is GdFeCo or T.
An amorphous perpendicular magnetization film such as dFeCo is used.

Transparent dielectric protective layers are added to both sides of the thin film recording layer of this magneto-optical optical disk in order to prevent deformation of the recording layer and provide a magneto-optical enhancement effect. Recently, in order to further enhance the enhancement effect, many have added a metal reflective layer to the top layer.

The material of the protective layer is 5iOz, ZnS, SiN.
is conventionally used, and is usually produced by a vapor deposition method or a sputtering method.

Development of the characteristics of such magneto-optical optical disks has hitherto focused on improving the characteristics of the recording film itself, such as improving the Kerr rotation angle θ. At present, recording films with a C/N ratio of 50 dB or more can be obtained.

Therefore, the focus of development has now shifted to improving recording sensitivity and repetition durability, and the optimization of the medium construction method of magneto-optical optical disks, especially the protective layer, is becoming a major issue. That is, although the above-mentioned characteristics strongly depend on the material of the protective layer, at present no firm guideline has been obtained regarding the influence of differences in the material and formation method of the protective layer on the disk characteristics.

Furthermore, magneto-optical media have the disadvantage that it is difficult to override recorded information compared to other rewritable optical recording media, such as phase change recording media. In order to overcome this problem, a magnetic field modulation override method or a light intensity modulation override method using a two-layer film has been proposed, but in the former method, the magnetic head equipped with a magnet is brought close to a few micrometers above the disk, so it is difficult to prevent the head from rolling. There is a risk of damage to the medium, and the latter has problems in that it is difficult to manufacture the medium and the margin for laser recording/erasing power is small.

(Problems to be Solved by the Invention) To explain more specifically, the protective film of the conventional magneto-optical optical disk has the following various problems.

■ If the dielectric protective film is formed by sputtering or vapor deposition, the deposition time is long because the film deposition rate is low.
■ The protective film often contains a large amount of residual film stress, which is the rate-limiting factor in the production of optical disks.
There were many cases where the characteristics deteriorated after about 0' cycles.■
In the case of sputtering, the temperature rises during film deposition, causing deformation of the plastic substrate and damage to its surface. ■ As mentioned above, magneto-optical disks are inherently difficult to override recorded information, so overriding is done using a magnetic field modulation method. If this is attempted, the magnetic head must be brought within a few micrometers from the disk surface, resulting in collision between the magnetic head and the medium, causing damage to the medium.

Such problems arose.

The present invention solves the above-mentioned problems with magneto-optical recording media by paying attention to the method of forming the protective film and its material, thereby achieving high sensitivity, excellent repeatability, and override. The object of the present invention is to provide a magneto-optical optical disc that is possible.

(Means for Solving the Problems) In the present invention, a method of forming a protective layer using chemical vapor deposition (CVD) using electron cyclotron resonance (ECR) plasma has been devised.

FIG. 4 shows an outline of the ECR plasma CvD apparatus.

This device consists of a rectangular waveguide 1 for introducing microwaves, a plasma generation chamber 2 and a sample chamber 3 connected to the rectangular waveguide 1, which satisfy cavity resonator conditions. Further, a magnetic coil 4 for applying a magnetic field is arranged around the plasma generation chamber 2.

Microwave (2,45G) introduced from rectangular waveguide l
Hz: The same frequency band as microwaves used as a heating power source for microwave ovens) to generate plasma. At this time, a magnetic coil 4 placed around the plasma generation chamber 2 generates electron cyclotron resonance (ECR).
) When applying a magnetic field (875 Gauss) that satisfies the condition,
A large amount of high-energy electrons that move in a circular motion can be generated by receiving the Lorentz force from a magnetic field. Furthermore, the divergent magnetic field leaking into the sample chamber 3 plays a role in accelerating ions appropriately.

(See Figure 4) Specifically, N2 plasma is generated in the plasma generation chamber 2, and 5iHa gas, for example, is introduced into the plasma outlet to efficiently decompose the gas, resulting in a gas phase reaction and a reaction on the substrate surface. A SiN film can be formed using the above steps. The above is the principle of ECR plasma CVD.

ECR plasma uses conventional RF plasma (13,56M
Since there are a large number of high-energy electrons moving in a circular motion compared to the 10-' Torr gas pressure, plasma with high activity (decomposition, excitation) and high ionization rate can be generated stably at a low gas pressure of about 10-'Torr. are doing.

Further, since the divergent magnetic field has the effect of pulling out ions into the sample chamber 3 and accelerating them appropriately (10 to 20 eV), it also has the feature of avoiding the problem of substrate damage due to excessive ion bombardment in RF plasma CVD.

These features provide the following effects.

(1) Because the reaction gas is decomposed efficiently, high-speed deposition is possible (approximately 10 times faster than sputtering)
.

(2) Ion bombardment to an extent that does not damage the substrate can promote the film formation reaction, and a dense, high-quality thin film can be formed without heating the substrate.

(3) Unlike the sputtering method, the gas is dissociated by plasma and a thin film is formed by a gas phase reaction, so the film quality largely depends on the production conditions such as the reaction gas flow rate, reaction gas ratio, and input power. Stress is compressive stress → free of stress →
It has the advantage of being able to control tensile stress over a wide range.

(4) Since thin films are essentially formed by CVD (vapor phase growth), depending on the manufacturing conditions, films can be formed that are hard, have excellent wear resistance, and have excellent mechanical strength with strong adhesion to the substrate. can.

This cannot be obtained by conventional sputtering methods or RF plasma CVD methods.

The ECR plasma CVD apparatus, which operates on the principle described above, is applied to the production of passivation films in semiconductor processes, and its usefulness is already being demonstrated (for example, J, J, ^, p, Vol.

22, No, 4. April, 1983 ppL
210-L212).

Now, by the ECR plasma CVD method used in the present invention,
If a dielectric protective film for optical disks is produced, the following effects can be considered.

(1) The time required to produce the protective film, which is the rate-limiting factor in producing optical disk media, can be reduced by about one order of magnitude (high-speed deposition).

(2) Since the substrate surface is not exposed to high-energy ions, there is less damage to the PC board (low-temperature production).

(3) It is possible to control film properties such as refractive index, internal stress, and adhesive force, and it is possible to form a high-quality thin film suitable as a protective film for optical disks (high-quality film formation by moderate ion bombardment).

(4) It is possible to create a hard, wear-resistant, and highly adhesive film;
It is suitable as a surface protective film to prevent damage to the medium from crushing of the magnetic head and medium in the magnetic field modulation override method.

(Example) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Figure 1 shows SiN as the material of the protective layer in one embodiment of the present invention.
This figure shows the dependence of the internal stress of the SiN il film formed on the substrate by the ECR plasma CVD method on the flow rate of the reactant gas when using the ECR plasma CVD method. The microwave power was fixed at 500 W.
The reaction gas ratio was kept constant at 5iHa:Nz=1:3, and the total flow rate of the reaction gases was varied.

The horizontal axis is the total flow rate of the reaction gas, and the vertical axis is the residual film stress, where 10 indicates compressive stress and - indicates tensile stress. From Figure 1,
The residual film stress is a relatively high compressive stress (> 5 × 10” dyn/C
1 l"), but decreases as the total flow rate of the reaction gas increases, and when the total flow rate of the reaction gas is 245 CCH, the tensile stress changes to about 5 XlO'dyn/cm".

Then, when the flow rate is further increased, compressive stress is again generated. Furthermore, there are also conditions that result in residual film stress O. That is, according to the 20ECR plasma CVD method, it is possible to control the stress of the thin film over a wide range by changing the total flow rate of the reaction gas. The composition of the film varies depending on the manufacturing conditions, but under these experimental conditions it is Si. N6
11~Si5°N,. The hydrogen content is within the range of 1
It was 0% or less.

Next relatively low compressive stress 3 x 10"dyn/cm"
(Production conditions: 500WSSiL: Nz=10S
An example in which a thin film having a CCM (CCM: 30 SCCM) is applied to a protective film for an optical disk will be described. Media configuration is PC
(Polycarbonate) Grooved substrate/SiN undercoat layer/GdFeC'o recording layer/SiN overcoat layer/metal reflective layer/epoxy resin layer for sealing.

The SiN undercoat layer has a thickness of 1100 nm, and the SiN overcoat layer has a thickness of 200 nm, and was manufactured by ECR plasma CVD method. The recording layer and the metal reflective layer were each formed with a thickness of 40 nm by RF sputtering.
m, 20no+ was produced.

Further, the sealing epoxy resin layer is prepared by spinner coating, and has a film thickness of about 10 .mu.-. FIG. 2 shows the repeated recording/erasing characteristics of the optical disk thus produced. Measurement was performed at a linear velocity of 20 m/s and a recording condition of 20 MHz%.
It was performed at 25ns% 10mW. In FIG. 2, the recording level and noise level are each shown in dB from the top.

From this, it can be seen that the initial characteristics are maintained even after repeated recording and erasing more than 1Oh times. That is, it was demonstrated that excellent repeatability characteristics can be ensured by using a SiN low residual stress protective film formed by ECR plasma CVD method. Table 1 shows the results of repeated evaluations of disks manufactured by varying the residual film stress of the protective film. When the compressive stress is as high as 7 x 10'dyn/cm2, the noise level increases at about 103 to 104. On the other hand, when the stress is approximately O, or when the tensile stress is 5
In the case of X lO"dyn/cI of about 112, no increase in noise level was observed up to about 106 to 107 cycles, indicating excellent repeatability.

Table 1 Relationship between residual film stress and repeatability Table 2 Deposition rate Next, Table 2 shows the results of comparing the film deposition rate with the conventional RF sputtering method. ECR plasma CVD
When using the RF sputtering method, approximately 1
It can also be seen that the digit deposition rate is fast and productivity is excellent.

(Note) ECRPCVD: ECR Braz? CVD
11 Rue - Repeated evaluations similar to those in Example 1 were conducted using a SiC film as the material for the protective layer of another example of the present invention. Media configuration is PC (polycarbonate) grooved substrate/S i
C undercoat layer/GdFeCo recording layer/Si
C overcoat layer/AI! This is a metal reflective layer/epoxy resin layer for sealing. SiC undercoat layer is 8
0 nm, and the SiC overcoat layer is 180 nm, and was produced by ECR plasma CVD method. The recording layer and the metal reflective layer were fabricated by RF sputtering to a thickness of 40 nm+ and 20 nm, respectively. The sealing epoxy resin layer was prepared by spinner coating and had a thickness of about 10 μm. Residual film stress of SiC film is 5X in compression
About 10" dyn/cm2 was used. Measurement was performed at a linear velocity of 20 m/s, recording conditions: 20 MHz, 25 ns, 1
2I11- was used. The results are shown in FIG. This shows that the initial characteristics are maintained even after repeated recording and erasing 107 times or more. Sunawachi Ec
It has been demonstrated that excellent cyclic properties can be ensured by using a SiC low residual stress protective film produced by the R plasma CvD method. In addition, the tensile stress is 7×10”dyn
Similar results were obtained by using a material with a diameter of 1.5 cm.

Since the SiC film has higher thermal conductivity than the SiN film, the recording sensitivity is slightly lower than when using the SiN film, but the mechanical properties such as hardness and Young's modulus are superior to the SiN film.
It seems that the repeatability is superior to that of the SiN film. Furthermore, the deposition rate of the SiC film by the ECR plasma CVD method is faster than that of the SiN film, and a deposition rate of 1100 n/win or more can be easily obtained (see Table 2), which has a very large effect on improving productivity.

Above, we have shown concrete results regarding the improvement of repetition durability and the improvement of deposition rate by the ECR plasma CVD method.

One possible reason for the improvement in repeated durability is that since a thin film with low residual stress was used, there is almost no release of thermal stress due to repeated recording and erasing, and irreversible deformation is suppressed. ECR plasma CV as described
It is thought that the unique characteristics of method D also contributed greatly. In other words, it is thought that the improvement in adhesion and tightness of the thin film due to moderate ion bombardment contributes to improving the mechanical strength of the protective film itself and the adhesion between the protective layer and the recording film. .

Therefore, in addition to SiN and SiC, the SiN,
When we fabricated a SiO□ film and a C-H film (hydrocarbon film), which have compressive and tensile stresses comparable to those of SiC, and applied them as protective layers, they were applied over 106 times and 10 times, respectively.
No deterioration of the initial characteristics was observed even after repeated recording and erasing seven times or more. Here, 5iOz is not limited to this, and the same applies to those with various O compositions such as 5iOz. Usually, a SiO□ film prepared by RF sputtering or vapor deposition is applied as a protective layer. Since the repetition durability in the case of
Similar to iC, an improvement in deposition rate was observed.

In addition, the protective film produced by the ECR plasma CVD method has excellent film density, so it has the effect of preventing moisture from penetrating into the medium. can be prevented.

In fact, for the medium of this example, 60°C 190%R
When an accelerated deterioration test was conducted under the high temperature and high humidity environment of H, no deterioration of properties was observed even after one month, and it was found that the material was excellent in terms of weather resistance.

Example 1 In this example, a medium subjected to the magnetic field modulation override method was designed and manufactured, and its characteristics were evaluated.

Media configuration is PC (polycarbonate) grooved substrate/Si
NSiN buffy N metal reflective layer/SiN undercoat layer/GdFeCo recording layer recording iN overcoat layer. The SiN buffer layer was prepared to strengthen the adhesion between the substrate and the metallic reflective layer, and had a thickness of 100 nm.
It is t. SiN undercoat layer thickness 200nmt
, SiN overcoat layer thickness was 300 nm, and both were manufactured by ECR plasma CDV method.

The recording layer and metal reflective layer are formed by RF sputtering.
They were fabricated with a thickness of 40 nm and 40 nm, respectively.

Characteristics of the magneto-optical medium produced in this way were evaluated using a magneto-optical head using a magnetic field modulation override method. As a result, when the flying height of the magnetic head above the medium was approximately 4μ, information was recorded and erased by overriding more than 106 times (overriding signals of 4T and 1.5T,
It was confirmed that a linear velocity of 10 m/s) was performed normally without deterioration of the C/N ratio.

Further, FIG. 5 shows the results of a contact start/stop test (CSS test) of the magnetic head. As shown in FIG. 5, it was found that no deterioration of the characteristics occurred even after C8S was repeated tens of thousands of times.

This is because the SiN film produced using the ECR plasma CVD method has excellent mechanical strength such as hardness, abrasion resistance, and adhesion, and has a sufficient surface area even when recording in which the magnetic head and medium are placed in close proximity, such as in the magnetic field modulation override method. This indicates that it plays the role of a protective film.

Therefore, by applying a protective film formed by the ECR plasma CVD method to a magneto-optical optical disk, it has become possible to perform the magnetic field modulation override method. The results of the C8S test described above are StC% 5tOz, CH film is Si
This was also obtained when using the same configuration as N.

By the way, regarding the adhesion force of the protective film, according to the adhesion strong motion evaluation test, the protective film obtained by the ECR plasma CVD method in this example has an adhesion strength of about 100 kg/cm'', which is about 100 kg/cm"
Protective film by F sputtering or vapor deposition weighs 50kg/
It was confirmed that the adhesion strength was far superior and mechanically strong compared to the adhesion strength of less than 2 cm.

(Effects of the Invention) As described above, the present invention provides ECI? By manufacturing using the plasma CVD method, ■ The residual stress of the thin film can be freely controlled, and by using a protective film with low residual stress, it is possible to prevent deterioration of disk performance due to repeated recording and erasing. Because it can be deposited at high speed, it can significantly reduce the time required to create the protective film, which has been the rate-limiting factor in optical disk manufacturing. ■ It can create a thin film with excellent adhesion and compactness, making it possible to create a protective film with excellent mechanical strength. It is easy to fabricate and is suitable as a surface protective film in the magnetic field modulation override method.It has a very large effect in contributing to improving the performance of magneto-optical optical disk media.

[Brief explanation of the drawing]

Figure 1 shows 5iN fabricated by ECR plasma CVD method.
F! Figure 2 shows the relationship between the residual film stress of the i film and the total flow rate of the reaction gas.
Figure 3 shows the evaluation results of repeated recording/erasing characteristics when fi film is used as a protective film.
Figure 4 shows the evaluation results of repeated recording/erasing characteristics when the WI film is used as a protective film. Figure 4 is a schematic diagram of the ECR plasma CVD device. Figure 5 shows the CSS of the medium of Example 3 using the magnetic field modulation override method. It is a figure showing the result of a test. l... Rectangular waveguide 2... Plasma chamber 3
...Sample chamber 4...Magnetic coil 5...
Sample Figure 4 6--Format button ↓ Figure 5 C3stnrD number (xtoooo)

Claims (1)

[Claims] 1. In a method for forming a protective layer used in a magneto-optical recording medium in which information is recorded and erased by irradiating a laser beam and causing a magneto-optical change in the irradiated area, the protective layer is The protective layer is formed using a cyclotron resonance (ECR) plasma CVD method and by controlling the CVD conditions, the deposition rate of the protective layer is increased and the residual stress in the protective layer is reduced. A method for forming a protective layer for a magneto-optical recording medium, characterized in that: 2. In a protective layer used for a magneto-optical recording medium that records and erases information by irradiating a laser beam and causing a magneto-optical change in the irradiated area, the protective layer is processed using the electron cyclotron resonance (ECR) plasma CVD method. By controlling the CVD conditions, the deposition rate of the protective layer can be improved, and the residual film stress of the protective layer can be reduced by compressing 1×1
0^9 dyn/cm^2 ~ stress 0 ~ tension 1 x 10^9
A protective layer for a magneto-optical recording medium, characterized in that the protective layer has a hardness of dyn/cm^2 or the surface of the protective layer is made of a hard and wear-resistant material. 3. In a protective layer used for a magneto-optical recording medium that records and erases information by irradiating a laser beam and causing a magneto-optical change in the irradiated area, the protective layer is processed using the electron cyclotron resonance (ECR) plasma CVD method. By controlling the CVD conditions, the deposition rate of the protective layer can be improved, and the residual film stress of the protective layer can be reduced by compressing 1×1
0^9 dyn/cm^2 ~ stress 0 ~ tension 1 x 10^9
A protective layer for a magneto-optical recording medium, characterized in that the protective layer has a hardness in the range of dyn/cm^2 and the surface of the protective layer is made of a hard and wear-resistant material.